Active matrix substrates used for liquid crystal display apparatuses and so forth include switching elements, such as thin-film transistors (hereinafter, referred to as “TFTs”), for respective pixels. It is reported that TFTs including an oxide semiconductor layer serving as an active layer (hereinafter, referred to as “oxide semiconductor TFTs”) are used as the switching elements. As the oxide semiconductors, for example, In—Ga—Zn—O-based semiconductors are used.
An oxide semiconductor TFT includes a protective film (passivation film) formed by, for example, a plasma-enhanced chemical vapor deposition (CVD) method or a sputtering method on an oxide semiconductor layer in order to inhibit the degradation of TFT characteristics with time. As the protective film, for example, a silicon oxide (SiO2) film is used.
An oxide semiconductor TFT containing an In—Sn—Zn—O-based semiconductor serving as an oxide semiconductor is disclosed (for example, PTL 1). In—Sn—Zn—O-based semiconductors can have higher mobilities than In—Ga—Zn—O-based semiconductors; thus, TFTs that operate at higher speed can be provided.